Disk Files for I/O

your variable

(of type ifstream)

your variable

(of type ofstream)

disk file“myInfile.dat”

disk file“myOut.dat”

executingprogram

input data output data

#include <fstream>

1

Disk I/O

To use disk I/O

Access #include <fstream> Choose valid identifiers for your file

streams and declare them Open the files and associate them with

disk names

2

Disk I/O, cont...

Use your file stream identifiers in your I/O statements(using >> and << , manipulators)

Close the files

3

Disk I/O Statements

#include <fstream>

ifstream myInfile; // Declarations

ofstream myOutfile;

myInfile.open(“myIn.dat”); // Open files

myOutfile.open(“myOut.dat”);

myInfile.close(); // Close files

myOutfile.close();

4

Opening a File

Opening a file Associates the C++ identifier for your file

with the physical(disk) name for the file– If the input file does not exist on disk,

open is not successful– If the output file does not exist on

disk, a new file with that name is created

– If the output file already exists, it is erased

5

Opening a File

Opening a file Places a file reading marker at the very

beginning of the file, pointing to the first character in the file

6

Stream Fail State

When a stream enters the fail state, Further I/O operations using that stream

have no effect at all The computer does not automatically

halt the program or give any error message

7

Stream Fail State

Possible reasons for entering fail state include: Invalid input data (often the wrong type) Opening an input file that doesn’t exist Opening an output file on a disk that is

already full or is write-protected

8

Run Time File Name Entry

#include <string>// Contains conversion function c_str

ifstream inFile;string fileName;

cout << “Enter input file name: “ << endl; // Prompt

cin >> fileName;

// Convert string fileName to a C string typeinFile.open(fileName.c_str());

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10

Names in Multiple FormatsProblem

You are beginning to work on a problem that needs to output names in several formats along with the corresponding social security number.

As a start, you decide to write a short C++ program that inputs a social security number and a single name and displays it in the different formats, so you can be certain that all of your string expressions are correct.

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Algorithm

Main Module Level 0

Open files

Get social security number

Get name

Write data in proper formats

Close files

Open Files Level 1

inData.open("name.dat")

outData.open("name.out")

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Get Name

Get first nameGet middle name or initialGet last name

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Write Data in Proper FormatsWrite first name, blank, middle name, blank, last name, blank, social security numberWrite last name, comma, first name, blank, middle name, blank, social security numberWrite last name, comma, blank, first name, blank, middle initial, period, blank, social security numberWrite first name, blank, middle initial, period, blank, last name

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Middle initial Level 2

Set initial to middleName.substr(0, 1) + period

Close files

inData.close()

outData.close()

15

C++ Program//*************************************************************// Format Names program// This program reads in a social security number, a first name// a middle name or initial, and a last name from file inData. // The name is written to file outData in three formats: // 1. First name, middle name, last name, and social security

// number.// 2. last name, first name, middle name, and social // security number// 3. last name, first name, middle initial, and social// security number// 4. First name, middle initial, last name//*************************************************************

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#include <fstream> // Access ofstream

#include <string> // Access stringusing namespace std;

int main(){ // Declare and open files ifstream inData; ofstream outData; inData.open("name.dat"); outData.open("name.out");

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// Declare variables string socialNum; // Social security number

string firstName; // First name string lastName; // Last name

string middleName; // Middle name string initial; // Middle initial

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// Read in data from file inData inData >> socialNum >> firstName >> middleName

>> lastName; // Access middle initial and append a period

initial = middleName.substr(0, 1) + '.';

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// Output information in required formats outData << firstName << ' ' << middleName << ' '

<< lastName << ' ' << socialNum << endl;

outData << lastName << ", " << firstName << ' '

<< middleName << ' ' << socialNum << endl;

outData << lastName << ", " << firstName << ' '

<< initial << ' ' << socialNum << endl;

outData << firstName << ' ' << initial << ' '

<< lastName;

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// Close files inData.close(); outData.close(); return 0;

}